The present invention relates to laser-based induction of arc discharge, and a laser based arc induction welding method and apparatus for arc welding a narrow gap.
Arc welding includes TIG (tungsten inert gas) welding, MIG (metal inert gas) welding, CO2, MAG (meal active gas) welding, and so on. Then, for moving an arc generated position in the MIG welding and so on other than the TIG welding, it is often the case that a torch 1 having a filler electrode 3 is moved with respect to a base material 2, which is to be worked, to move the arc, as illustrated in FIG. 15. For reference, in the case of the TIG welding, an electrode is separated from a filler, so that the tungsten electrode is moved with respect to a base material, which is to be worked, to move an arc. This is because the TIG welding uses non-consumable electrode, while the MIG welding and so on use a consumable electrode.
Also, for example, in a method described in JP-A-5-146877, a feeding wire 19 is bent by a filler bending gear 6 to move an arc discharge 4 for welding, as illustrated in FIG. 16.
Also, as illustrated in FIG. 17, there is a method in which the position of an arc discharge 4 is moved using a filler 3 fed by a filler feeding hose 11 as an eccentric tip is rotated by a motor 9 and a belt 10, to form a welding bead 7 for welding.
Further, JP-A-62-263869 describes an arc welding method which induces an arc using a laser.
Also, for welding a groove using the TIG welding or the like, a torch 1 is moved for waving, as illustrated in FIG. 18, to weld the groove by means of an arc discharge 4 generated between a filler electrode 3 and a base material 2 which is to be worked.
For welding a narrow gap, the torch 1 is inserted into the gap for welding. However, since the torch 1 cannot be waved, the welding is carried out by a method as described, for example, in JP-A-5-146877.
Specifically, as illustrated in FIG. 19, a wire fed by a filler bending gear 6 is bent to form a welding bead 7 between base materials 2 within the groove for welding. Reference numeral 8 designates a backing jig.
Also, as illustrated in FIG. 20, an eccentric tip is rotated by a motor 9 and a belt 10 to rotate a filler supplied from a filler supply hose 11 to control the direction of a discharge 4.
However, even in the method of moving the torch in the above-mentioned prior art, and wire bending and rotated eccentric tip described in JP-A-5-146877, it is not always easy to induce an arc discharge to a precise position due to the shape of a target work, electromagnetic influence, and so on.
Also, a method described in JP-A-62-263869, which is an arc induction method for inducing an arc using a laser, is not sufficient to always reliably induce an arc to a precise position.
Particularly, in the prior art, when an arc discharge electrode (filler electrode) 3 approaches a side wall of a base material 2 in narrow gap welding, a plasma 5 is generated by an arc discharge between the electrode 3 and the side wall of the base material 2 as illustrated in FIGS. 21 and 22, resulting in a problem that the welding cannot be stably carried out, and so on.
Also, either of other arc welding such as a bending wire method, an eccentric torch rotating method, and so on does not precisely induce an arc discharge to a position to be welded, so that they have a problem in that an arc discharge takes place at a position different from a welding intended position due to the shape of a work and the influence of an electric field so that stable welding cannot be carried out.
Also, since the arc discharge cannot be precisely moved into a narrow gap, a portion A indicated in FIG. 21 is left unwelded, resulting in a problem of defective welding.
Specifically, as illustrated in FIG. 23, when the distance xcex1 between an electrode 3 and a side wall of a base material 2 is smaller than the distance xcex2 between the electrode 3 and the bottom of a groove of the base material 2, an arc discharge plasma 5 is generated on the side wall during arc welding.
For this reason, as illustrated in FIG. 24, the groove side wall is welded by a welding metal 30, but the bottom of the groove is left as an unwelded portion 31.
For preventing the bottom of the gap from being left unwelded, it is contemplated to extend the gap angle from 45 degrees to approximately 90 degrees, in which case, however, a welded portion is largely increased and a longer time is taken for welding. Further, a larger amount of filler material to be melted must be consumed, thereby increasing a welding cost.
As another method, it is contemplated to gouge an unwelded portion from the back surface after a welding operation to again weld the unwelded portion from the back surface.
However, this method requires an additional time for gauging and repetitive welding, and causes an increased cost. Further, the gauging from the back surface itself may be difficult in some cases.
In the prior art, an example of inducing an arc with laser is described in JP-A-62-263869 which, however, is not sufficient to always reliably induce an arc to a precise position. Specifically, after an arc is generated at a desired portion by means of laser, a plasma caused by the generated arc acts to give rise to a phenomenon illustrated in FIG. 23.
Also, as described in xe2x80x9cWeaving of Arc due to CO2 Laser,xe2x80x9d Abstract of National Conference of Institute of Welding, Vol. 60 (""97-4), a fast surface treatment is accomplished by a laser included TIG arc.
However, in the fast surface treatment relying on the laser induced TIG arc, a wide gap exists between a TIG electrode and a work, and a moving speed is so high that this is not a region which can be welded by a TIG arc alone, and in which the directivity of the TIG arc is lost near the base material. For this reason, a precise induction of an arc in the TIG welding is difficult.
It is a first object of the present invention to provide a laser-based arc induction method which is capable of precisely producing a stable arc discharge at a desired position, stably inducing an arc discharge to an arc discharge position by means of a laser, and stabilizing the arc discharge itself.
It is a second object of the present invention to provide a laser-based arc induction welding method and apparatus which are capable of precisely performing stable arc welding at such positions as the bottom and a corner of a narrow gap, and capable of stabilizing an arc discharge.
To achieve the above objects, the present invention is configured in the following manner.
(1) In a laser-based arc induction method for irradiating a laser to a work intended position on a surface of an object intended for working, and inducing an arc discharge generated between an arc electrode and the object intended for working to take place between the arc electrode and a position irradiated with the laser, an arc discharge voltage supplied between the arc electrode and the object intended for working is a periodically changing voltage.
(2) Preferably, in the laser-based arc induction method of (1) set forth above, the periodically changing voltage is an alternating voltage.
(3) Also, preferably, in the laser-based arc induction method of (1) set forth above, the periodically changing voltage is a pulsed voltage.
(4) Also, preferably, in the laser-based arc induction method of (3) set forth above, a pulse interval of the pulsed voltage is 0.1 ms or more.
(5) In a laser-based arc induction welding method, a periodically changing voltage is applied between an arc electrode and an object intended for welding, a laser is irradiated to a welding intended position on the object intended for welding to generate a plasma and metallic vapor when arc welding is performed, and an arc discharge is induced to the welding intended position irradiated with the laser to perform the arc welding.
(6) Preferably, in the laser-based arc induction welding method of (5) set forth above, the periodically changing voltage is an alternating voltage.
(7) Also, preferably, in the laser-based arc induction welding method of (5) set forth above, the periodically changing voltage is a pulsed voltage.
(8) Also, preferably, in the laser-based arc induction welding method of (5) set forth above, the object intended for welding is a welding intended portion within a narrow gap.
(9) Also, preferably, in the laser-based arc induction welding method of (5) set forth above, the laser is swung with respect to the welding intended position.
(10) A laser-based arc induction welding apparatus comprises voltage applying means for applying a periodically changing voltage between an arc electrode and an object intended for welding, laser irradiating means for irradiating a laser to a welding intended portion within a narrow gap of the object intended for welding when an arc welding is performed, and control means for controlling operations of the voltage applying means and the laser irradiating means, wherein the laser is irradiated to the welding intended portion of the object intended for welding to generate a plasma and metal vapor, and an arc discharge is induced to the welding intended portion irradiated with the laser to perform the arc welding.
(11) A laser-based arc induction welding apparatus comprises voltage applying means for applying a periodically changing voltage between an arc electrode and an object intended for welding, laser irradiating means for irradiating a laser to a welding intended portion within a narrow gap of the object intended for welding when an arc welding is performed, weaving means for weaving the laser with respect to the welding intended position on the object intended for welding, and control means for controlling operations of the voltage applying means, the laser irradiating means and the weaving means, wherein the laser is irradiated to the welding intended portion of the object intended for welding to generate a plasma and metallic vapor, and an arc discharge is induced to the welding intended portion irradiated with the laser to perform the arc welding.
(12) Preferably, in the laser-based arc induction welding apparatus of (10) or (11) set forth above, the periodically changing voltage is an alternating voltage.
(13) Also, preferably, in the laser-based arc induction welding apparatus of (10) or (11) set forth above, the periodically changing voltage is a pulsed voltage.
Since the arc discharge voltage is a pulsed or alternating periodically changing voltage, after the generation of an arc discharge, induced by the laser, is started at the laser irradiated position, the arc discharge voltage is reduced before the arc is induced to a position different from the laser irradiated position due to a plasma generated by the arc discharge to extinguish or mitigate the plasma generated by the arc discharge. Then, after the plasma generated by the arc discharge is extinguished, the arc voltage is increased to continue the arc welding at the position irradiated with the laser.
Also, generally, a plasma generated by an arc discharge extinguishes in about 0.5 ms after the arc discharge level decreases. Therefore, the pulse interval of the pulsed arc discharge voltage may be 0.1 ms or more.